cyl·in·der (sĭlˈən-dər)

1. The surface generated by a straight line intersecting and moving along a closed plane curve, the directrix, while remaining parallel to a fixed straight line that is not on or parallel to the plane of the directrix.
2. A solid bounded by two parallel planes and such a surface, especially such a surface having a circle as its directrix.
3. A cylindrical or rodlike renal cast.
4. A cylindrical lens.
5. A cylindrical metal container for gases stored under high pressure.